1. Field of the Invention
The present invention relates to a balun (balun transformer) that performs conversion between unbalanced and balanced signals, and in particular relates to a thin film balun that is formed by a thin film process advantageous for smaller and thinner models.
2. Description of the Related Art
A wireless communication device includes various high frequency elements such as an antenna, a filter, an RF switch, a power amplifier, an RF-IC, and a balun. Of these elements, a resonant element such as an antenna or a filter handles (transmits) an unbalanced signal which is based on a ground potential, whereas an RF-IC which generates or processes a high frequency signal handles (transmits) a balanced signal. Accordingly, when electromagnetically connecting these two elements, a balun that functions as an unbalanced-balanced converter is used.
Recently, there is a demand for smaller and thinner baluns for use in wireless LAN devices, mobile communication devices such as a mobile phone and a portable terminal, and so on. As one of such baluns, for example, Japanese Patent Application Laid-Open No. 2006-270444 and Japanese Patent Application Laid-Open No. 2001-168607 each propose a balun having a structure in which a capacitor is connected to at least one of an unbalanced circuit and a balanced circuit.